Electrocardiograph with continuous record means



March 10, 1953 N' MARCHAND 1 2,630,797

ELECTROCARDIOGRAPH WITH CONTINUOUS RECORD MEANS Filed July 2, 1949 A TTORNE YS Patented Mar. 10, 1953 EiLEcTaocARDIoGRAPH wrml CON-` TINUOUS Recon-D MEANS Natharierchae, New Ydrk, N. Y., a'ssligni: t6 Technicon Cardiograph Corporation, New York, N. Y., a corporation of New York Application Jury z,- 1949, seriztlNq'.y 1oz-,ses is" claims. (o1. 12s-2.06)

The present invention relatesv to-'electroecardiographs and to electrical and electronicv circuitsV therefor.

ln my application Ser. No'. 762,633yfi1e'd July 22, 1947, I have disclosed: and claimed a" multiple lead electro-cardiograph operable to'produce` simultaneously and directly' on a' recordv web or sheet a plurality of graphs or traces of body voltage variations transmitted from'the'subject hy the several leads,respectively,and to produce said graphs or traces on' the web or record sheet in such manner that'they'all have an identical time relation withrespect" to each other. For example, the standardfor inter-extremity potentials, namely','the left-arm-right-arm voltage .fariations, the right=armleftleg voltage variations, the left-armfleftdeg voltage-variations are all recorded simultaneouslyV on the record sheet in the same timerelation sothatthe physician, cardiologist, or diagnosticianfcanobtain not only the information as revealed bylsaid three dierent voltage variations considered separately but also as revealed by said three' voltage `variations considered in their correlated -aspects atv any inn stant of time along a common time co-ordinate of the three cardiograms.. In this connection it will he understood that even when cardiograms corresponding to different leads' are obtained in immediate succession, thek cardiologist cannot be certain that the condition ofthe subjects 'heart not changed inthe-time intervals between the taking of the several cardiograms, even if such intervals are very short. Hence, he' is not able to correlate the information revealed by thethree dierent lead cardiogra'ms, 'with'the same degree oi certainty of correct analysis which is possible When the several vcardiograrns are obtained at the same time.

In the apparatus described in my "above mentoned application,-provision is made not only for recording the standardv (inter-extremity) potentials, referred to abovef but also for recording the chest voltages," and' for recording' the extremity potentialswith reference to a point of zero potential. Aselector switch'is provided in apparatus for connecting thev differentsets ci leads to the companion channels, respectively,

each of which includes'electronic amplifying means for amplifying the'y body voltagesV transmitted to said channels in accordancewith the setting or" the selector switch." Since the various leads connected to the patient introduce the patients skin voltages rinto'theamplifying channels: these voltages tend to become transient'upon the actuation of the'selectorswitch-during the investigation operation"duectortheir effect upon4 the capacitors in said channels. In vorder to stabilize the action of thev ampliersin the various channels before operating fthe 'marking elements of the recorderf'a"'tineedelay circuit "is provided, said circuit operating"l/Wheneverthe" selector svvitcli is actuated the comcination of leads which .areonnected to the channels, to prevent the marking; elements from.

operating until theaction of.theampliiers in the several channels become stable., Although the delay introduced by said,,timeedelayl circuit may loeV less than a niinutaethevcondition of the subjects heart may change duringeachof these` intervals,'as theselector switch is'rotated through its various positions.` This is Amost mevident in taking cardiograms during an exercise test where.

various voltagecombinations are to be recorded immediatelyl upon the Acessation O Lthe, exercise. TheV time-,delay introducedoeach time the selec-v tor switch'is operated may tendto ,aect the accuracy of the cardiogramv since ,the patients heart'is returning topa conditionofl normal paf tient activity', or rest, duringfthe delay periods,

and each successive; switching; operation, .by

introducingu an additional delay, results inv a cardiogram during aperiodfarther removed `from the condition of the patients heart during 'the exercise period. .Y i

In accordance Withthe present, invention and pursuant to the primaryfobject thereof, provision is made to permit the recording ,0i acardiogram immediatelyfaiter switching f rjoinone .comhination ofleads to another without the customary time .delay or. Waitingiperiod.N

Another p object is i to provide means for preventing' the` introduction of transient voltages into the electrofcardiograph equipment through the patient leads.

The-above and other advantages of the present inventionvvill be, fully understood from -the following ydescription con sidered in` connection with.. the', accompanying drawing which schematically illustrates aj multiple lead electrocardiograph' embodyingV the present invention. Referring to .the vdrawing"herein, theelectrocardiograph of the present invention comprises the continuous Vrecord switch lo connected to a'plu` rality of connecting points constituting the patient terminals, herein:designated PI, `l?2,P3RA, LA, LL, Ri'. It'will'b'e understood that said connect# ing pointsfare adapted to he connected ley-suit-Y able conductors and; companion electrodes (not shown) tofdiilerent parts, respectively', of' the subjectiwhoseheart condition is to`be investigated. .The terminal 'RListo he Vconnected .to the right leg of the j subject` and is grounded Vas shown." The 'terminalsRA LA and LU are the extremity terminals v,forv connection, respectively. tothe subjects right,arm,left arm and left leg,l

in accordance withknown l principles of cardiolo- The terminals PLJPZ and P3 are the precordial terminals; Thepatient .terminals'are provided wth' nlter networks y I2' ,and are con- CRA-SOLA" "and CLL, resp'ectvely,v of the switch'.

vosiects;v features andv 3 The switch ill comprises the switch sections ISA, 56B, mC, itD, Iii-E, HBF, 523C, ici-I, and Ici.

Switch selection iA comprises the stationary input contacts CLA, CRA and CPI, and the com panion movable contact ASA which is connected to the output terminal I. Switch section tcl8 comprises the stationary contacts CLL, CLA and CP2 and the companion movable contact 55B which is connected to the output terminal Eil. Switch section #9C comprises the interconnected stationary contacts CLL, the stationary contact CPS and the companion movable contact BEC which is connected to the output terminal 22. Switch sections IUD, WE and Ich comprise an unconnected stationary contact which represents an oir position, as illustrated in the drawing, as well as the interconnected stationary contacts WT and the companion movable contacts 613, liE and F, respectively. Switch section 10G comprises the stationary contact CLA, the interconnected stationary contacts VF and the companion movable contact 46G- which is connected to the output terminal 24. Switch section lill-l comprises the stationary contact CRA, the interconnected stationary contacts VL and the companion movable contact cti-l. which is connected to the output terminal it. Switch section lill comprises the stationary contact CRA, the interconnected stationary contacts VR, and the companion movable contact @5I which is connected to the output terminal It. All of said movable contacts are ganged for simultaneous operation to the three settings of switch lll, as represented by the three stationary contacts at each of its component switch sections. As will hereinafter more specically appear, the pa tient terminals LA, LL and RA are also connected by the movable input contact members MD, iE and 46E, respectively, to form a conimon terminal at the interconnected contacts WT, A

known in the art of cardiology as the Wilson connection, the central terminal, or the indiiern ent electrode of zero potential. The movable contact members, dA and icl, 55B and tSH, 116C and 46C, are connected in pairs tothe three pairs of output terminals ifi-Iii, iii- 26, and 22-24, respectively, of the switch it. For eX- ample, in one setting of the switch Iii, the LA and RA leads are connected to output terminals it and it, respectively, the LL and RA leads are connected to the output terminals i8 and 2t, respectively, and the leads LL and LA are con nected to the output terminals 22 and 2t, respectively. In other settings of the switch, the three leads are connected to different output terminals of the switch, as will appear.

The three leads, thus connected to the selected output terminals, are connected by means oi the conductors 25-28, Sile-32, and 3ft-S5, respectively, to three diierent channels A, B, and C, respectively.` Each of said channels includes electronic amplifying means for amplifying the body voltages transmitted to said channels by said three leads from across three pairs of difierent parts of the subjects body. The electrical circuits of these channels preferably are all alike, and may be of any suitable type, for example, as in U. S. Patent No. 1,647,710 to H. E. Nichols, or of the type illustrated and described in my previously identied application. As these electrical circuits, per se, do not constitute the present invention, they are not illustrated or described herein. If desired, each channel may be provided with a step controlled sensitivity device, such as is described and claimed in my application Ser. No. 14,558, led March l2, 1948, wherebythe sensitivity of all the channels may be altered not only simultaneously but substantially instantaneously from one sensitivity to another, without loss of record of intermediate heart beats and without re-adjustment of any of the other controls of the amplifier.

The output terminals of said channels are connected to the driving coils DCA, DCB, and DCC, respectively, of the magnetmnotive devices which are provided in the apparatus for operating the recorder. These magneto-motive devices include a strong permanent magnet, shown schematically as three permanent magnets 38A, 38B, and 33C. As illustrated and described in my above mentioned applica-a tions, the driving coils are mechanically connected individually to suitable pens or marking elements which are schematically represented by the'resistances MA, MB and MC. It will be understood that such marking elements operate on a suitable recording material to record the voltage variations supplied to said channels and amplied by the amplifying means provided therein, as hereinbefore indicated. As is well known to those skilled in the art, such recording material may be preferably, but not necessarily, chemically treated paper of a known type and when such paper is used the pens or marking elements are electrically heated, as indicated by the resistances designated by the foregoing reference characters MA, MB, and MC which schematically represent electrically heated marking elements. As will be readily understood the paper is affected by the heat of said elements whereby visual records are produced directly on a length oi said paper during the movement of the latter in the direction of its length. The connections or" the driving coils to the companion marking elements are indicated schematically by the dote ted lines 116A, 46B, and 46C, and are illustrated and described in my first above mentioned application. As indicated, a synchronous motor c2 is provided for moving the recording material' or paper at uniform speed in the direction of its length. The motor is preferably energized by 60 cycle alternating current at 110 volts, and a step-down transformer T is provided for supplying heating current to the resistances of the marking elements or pens MA, MB, and MC. An adjustable resistance R is provided in the primary circuit of the transformer for regulating the heat of said marking elements.

The continuous record switch Id comprises the switch sections HBA, itB, iilC, liiD, UEE, IiF, lG, I'ii-, and E01. Lead 44A connects the patient terminal Pi to stationary contact CPE of section liA. Lead 4MB connects the patient terminal P2 to stationary contact CP2 of section icB. Lead MC connects the patient terminal PS to stationary contact C123 of section iSC. A lter unit l 2 is interposed in each oi' said leads at a point between each patient terminal and the companion stationary switch contact. Lead [iiD connects the patient terminal RA to stationary contact CRA of section iiaA. Lead clin connects the latter stationary contact to stationary contact CRA of section itl and to lead i513 which is connected to stationary contact CRA of section Il-I. A lter unit l 2 is interposed in lead siiD between patient terminal RA and contact CRA of section HBA. Lead MF connects patient terminal LA to stationary contact CLA of section iOA. Lead '35C connects lead MF to stationary contact CLA of section HiB and lead 25D connects said stationary contact to stationary contact CLA of section NG. A iilter unit il lis interposed in lead MF between patient terminal LA and contact CLA of section IDA, said lter unit also being interposed between the latter patient terminal and lead 45C which is connected as described. Lead 44H connects patient terminal LL to stationary contact CLL of section lIlB. Lead 45E connects lead 44H to the interconnected stationary contacts CLL of section IflC. A filter unit t2, is interposed in lead MH between patient terminal LL and stationary contact CLL of section H1B, said filter unit also being interposed between the latter patient terminal and lead 45E which is connected as described. Lead ME is connected between patient terminal RA and the movable contact 46E" of section EDF'. A resistor t8' and a filter unit I2 are interposed in lead 44E between patient termineral RA and movable contact 415?. Lead MG is connected between patient terminal LA and' movable contact 45D of section IDD. A resistor A8 and a filter unit l2 are interposed in lead MG between patient terminal LA and movable' contact ilD. Lead MI is connected between patient terminal LL and movable contact 45E oi" section lilE. A resistor llS and a filter unit t2 are interposed in lead MI between patient terminal LL and movable contact 46E.

Each filter l2 comprises, ashere shown, a capacitor IZA connected in series, in each of the leads MA through 441, said capacitor being in circuit, in each of said leads, between the patient, to whom the patient terminals are connected by suitable means (not illustrated), and the input side of the respective switch sections toY which said leads are connected. More speciiically, it will be noted that capacitors I2A in leads MA, 44B and 45C are connected between patient terminals Pl, P2 and P3, respectively, andthe iixed contacts CPI, CP2 and CP3, respectively, of the switch sections I UA, HiBV and IBC, respectively. The fixed contacts constitute the input sides of said sections, the movable contacts 45A, 46B and 46C thereof, being connected to output terminals l, IS, and 22, respectively, and' constituting the output sides of said switch sections. In the same manner it will be noted that capacitor IZA in lead MD is connected between the patient terminal RA and xed contacts CRA of swi ch sections IllA, ltI and lBH, that capacitor IZA in lead MF is connected between patient terminal LA and each of iixed contacts CLA of switch sections IGA, IBB and H3G, the movable contact lG in the latter switch section being connected to output terminal 2li, constituting the output side of said section. Similarly, capacitor I2A in lead is connected between patient terminal LL and the nxed contacts CLL in each of switch sections lB and iC, said contacts being in the in'- put sides of saidswitch sections. Reierring now to switch sections IUD, IUE and HBF, it will be noted that in these sections the movable contacts 48D, 55E and BSF are connected to the patient terminals LA, LL and RA, respectively, through leads MG', MI, and 44E, respectively, as described, said movable contacts therefor constituting the input sides of their respective switch sections. Each of the sections D, SEE and it? has a pair of fixed contacts WT which are interconnected. Said interconnected contacts WT are all connected to the lead 58. Said lead is also connected to the interconnected pair of fixed contacts VF'of switch section IDG, to the inter connected pair of fixed contacts VL of section HJH, and to the interconnected pair of fixed contactsVR of section IUI. The movable contact ESG is 'connectedthrough lead 41A to output terminal 24. 'Ihe movable contact IGI-I is connected through lead 41B to output terminal 2B, and the movable contact 461 is connected through lead 57C to output terminal I6. Therefore, it will be apparent that when the movable contacts ASI. 46H and AGG engage ther fixed contacts VR, VL and VF, respectively, the stationary' contactsWT of sections IilD, Ill-E and HIB"v are connected to output terminal I6 through contact IGI, to output terminal 28 through contact 46H, and to output terminal 24 through contact 46G. It will be noted that capacitors I2'A in each ofA leads 44E, liG and 441, being connected tothe movable contacts fiF, 46D and #GE-,respectively are therefore also connectedto the' input sides ofi theA respective switch sections. Therefore, it will be apparent that no capacitor IEAV is connected directly to one of the output terminals of switch i@ or to the side of a switch sectionwhich connects to an output terminal.

In addition to capacitor IZA, each filter I2 is provided with a resistor IZB connected in shunt between the side of the-capacitor remote from its respective patient terminal and ground.- Values for each lter component'are chosen to provide a predetermined time constant'for the filter action such that frequencies close to a direct-current condition will be blockedfrom feed-ing into the electro-cardiograph beyond switch l0, as willA said leads being connectedto the movable con-v tacts liti?, 55D andv 46E', respectively, of switchv sections HBF, 10D and I'ELre'spectively. It will. be noted that there is no circuit formed:l in sta-4 tion of these switch sections. However, corn' tacts WT are interconnected in eachone of these switch sections and these interconnected con-l tacts are all connected to lead 501 As is well known to those skilled in the art of cardiology, the Wilson terminal is formed by" placing a resistor in series in each one offthree' leads.. OneI end of each leadv is connectedto a1 patient ex tremity terminal, andthe other` endsof said three leads are joined to forniV a: common terminal which is known as'the Wilson terminal'. Therefore, it will be apparent that in stations? and 3 of switch sections It?, IDand IGE, with the movable contacts llEF, 45D and 46E each engaged with a stationary contactWT'whioh is connected to lead Evil, the leads 44E, MSF, and MG are all joined at one end thereof.; The other ends of said leads are connected to the patient terminals RA, LL, and LA, respectively, and each of said leads is provided with a resistor 481 of a predetermined value inseries therewith. Therefore, it will be understood that the Wilson'terminal is formed when switch sections IIJD, IUE. and it? are moved to stations 2 or 3 thereof. Byrma'king each resistor lil` havethesam'e'- resistance value, it' is apparent that the `Wilson?terminal provides an equipotential or reference pointlfor. the use of the cardiologist.

It will heV noted that all the movable contacts of the various switch sections are mechanically ganged for conjoint movement. For convenience it may be assumed that-all ofthe movable' contacts move rectilinearly in'= moving toand from each of the severalstationsl, 2*, andA 3`.V

At station l, the movablecont'acts for the three channels are connected-tofthe-LA-EA, LL-RA, and'LL--LA patient terminals t'o'fcrml the standacsogrc'? ard leads, designated in cardiology as I, IIand III.

At station 2, the movable contacts for the three channels are connected to record the unipolar limb leads, designated in cardiology as VR, VL and VF. Lead VR records the potential between the right arm and the Wilson terminal. Lead VL records the potential between the left arm and the Wilson terminal, and lead VF records the potential between the left leg and the Wilson terminal. The circuit for recording the VR lead includes the patient terminal RA, lead MD, engaged contacts CRA and 46A of section IBA, output terminal id connected to contact 45A, and line 25 from terminal l5 to channel A which is also. connected to patient terminal RA through line 2t, output terminal It connected to the engaged contacts i161 and VR of section lii, said contacts beingjconnected by lead t to the previously described v Wilson terminal connection, which, in turn, is connected through lead ME to patient terminal RA, and through leads 4G and ici to the patient terminals LA and LL, respectively. The circuit for recording the VL lead includes the patient terminal lead lead fiflF, engaged contacts CLA and B of section iB, output terminal iilconnected to contact 56B, and line 3 to channel B which is also connected to patient terminal LA through line output terminal 2t which is connected to engaged contacts and VL of section itil-I, said contacts being connected by lead 50 to the previously described Wilson terminal connection which, in turn, is connected to each of the patient terminals LA, RA and LL, as previously described. The circuit for recording the VF lead includes the patient terminal LL, lead 44H, engaged contacts CLL and @5C of section ISC, output terminal t2 connected to Contact 46C, and line 34 to channel C which is also connected to patient terminal LL through line 3d, output terminal 24 which is connected to engaged contacts LlGG and VF of section H3G, said contacts being connected by lead 5t to the previously described Wilson terminal connection which, in turn, is connected to each of the patient leads LL, LA and RA, as previously described. Thus, at station 2, the voltages between the right arm and a common point, essentially at Zero potential, are transmitted over channel A to the companion recording element. Said common point is the Wilson terminal to which the three extremities are connected, each through a resistor Aid. At the same time the voltages between the left arm and the common Wilson terminal, `connected to the three extremities, are transmitted over channel B to the companion recording element of the recording apparatus. Also at the same time the voltages between the lett leg and the common Wilson terminal, connected to the three extremities, are transmitted over channel C. Thus, the potentials are transmitted simultaneously to the three channels, respectively, when the movable switch contacts are at station 2 so that said potentials can be recorded simultaneously by the corresponding marking elements in the recording web in the same time relation.

At station 3, provision is made for recording three unipolar precordial or chest leads which record the potentials from the anterior surface oi the heart. The Wilson terminal is used in recording the precordial potentials. At station 3, the circuits for the precordial leads are completed in the following manner: The precordial patient terminal PI, is connected by lead dflA to engaged vcontacts CPI and tA of section IEiA, said contacts being,,Qm1eied, w;0utput terminal '4 which is connected to channel A by line 26, said channel being also connected through line 2S to output terminal i6 which is connected to engaged contacts fit1 and VR of section IIJI which, in turn, are connected through lead 5G to the Wilson terminal which, in turn, is connected to the three extremity terminals, as previously described. The precordial patient terminal P2 is connected by lead 44B to engaged contacts CP2 and 45B of section IBB, said contacts being connected to output terminal I3 which is connected to channel B by line Sil, said channel being also connected through line 32 to output terminal 2] which is connected to engaged contacts 45H and VL of section itH which in turn, are connected through lead 50 to the Wilson terminal which, in turn, is connected to the three extremity terminals. as previously described. The precordial patient terminal PS is connected by lead MC to engaged contacts C133 and 6C of section IC, said contacts being connected to the output terminal 22 which is connected to channel C by line 34, said channel being also connected through line 36 to output terminal 2d which is connected to engaged contacts @EG and VF of section ISG which, in turn, are connected through lead 5t to the Wilson terminal which, in turn, is connected to the three extremity terminals, as previously described.

As previously indicated, the patients skin voltages charge the capacitors in the various amplitying channels. Upon the actuation of the selector switch during the operation of the electrocardiograph, these charges become transient and tend to render the ampliers in the various channels unstable as they pass through the channels.

in accordance with the present invention, the various switching operations, described above, can take place without requiring a waiting period before the recorder can become operative, the filters i2, by preventing the generation of transient effects in the channels upon the actuation of the selector switch, permitting a continuous recording operation. As is well known to one skilled in the art, each iilter I2 has a time-constant which is a function of the respective Values of the .lter components. Since the transient voitages, to which the apparatus is subjected, result from the patients skin voltages which are extremely low frequencies approaching directcurrent, said frequencies being of the order of a fraction of a cycle, the time-constant of the filter i2 should be such that only these extremely low frequency variations, close to direct-current will be blocked from passing through the apparatus without, however, blocking the desired extremely low body voltage frequencies. It has been found that a filter l2 constituted, for example and not by way of limitation, by a one microfarad capacitor and a resistor having 4.7 megohms of resistance, will provide a time-constant that will `cause capacitor iZA to block these unwanted skin voltages.

in taking an electro-cardograph recording, leads, provided at one end with electrodes for securement on the patients body, are connected at their other ends to the terminals PI, P2, P3, RA, LA and LL, respectively. Therefore, it is apparent that capacitors I 2A, which are connected between said terminals and the input terminals of switch iii', will be charged by the patients skin voltages which are transmitted by said electrodes to said input terminals. This charge will be present at all times during the cardiac investigation since the filters I2 are conneared at the input side of switch in and not between the switch and the amplifying channels. Therefore, the switch never interrupts the circuits between the patient and the lters l2, as would be the case if the lters were connected to the output side of the switch. In the latter case, the iilter capacitors are charged when the circuit is completed through the switch to the patient. However, when said latter circuit is interrupted by the operation of the switch, it is apparent that the charged capacitors are disconnected from the source of skin voltage, even though this may be momentarily, and will discharge into the amplifier channels. This discharge produces transients which render the amplier channels inoperable for as much as several seconds until the transient effects pass therethrough. However, by connecting the lters at a point electrically remote from the companion amplifying channels, lthat is, between the patient and the input side of the switch lll, so that they are always being charged, regardless of the condition of the switch, and by providing a proper time constant. the switching operation will not result in the discharge of the capacitors into the amplifying channels. Consequently, transient voltages which render the apparatus temporarily inoperable for recording purposes will not be generated. Therefore, the switching operations can take place without requiring a waiting period.

Due to the presence of the resistors d8 which, as previously described, are joined to form the Wilson connection, the components of `filter l2 in leads 44E, MG and MI are given Values different from the values of the lter components in leads 44A, 44B, 44C, 44D, MF and MH. This is necessary to compensate for the presence of resistors 48 which affect the time constant of the associated lters. It has been found, for example, that using 5600 ohm resistors for the resistors AB, and assuming that filters I2, in all those leads not having a resistor 48, are comprised, for example, by a one microfarad capacitor and a 4.7 megohm resistor, that the filters in those leads having the resistors 48, can, for example, comprise a one microfaradicapacitor and a l5 megohm resistor. It will be understood, of course, that all component values are merely illustrative and have been included only by way of illustration.

The continuous-record switch may be provided for the electrocardiograph instead of or in addition to the lead selector switch shown in my above mentioned applications Ser. No. 762,633, iiled July 22, i947, and Ser. No. 14,558, filed March l2, lf3/i8. When provided for the electrocardiograph which is provided with said lead selector switch, as shown in my prior applications, just referred to` either said lead selector switch or said continuous-record switch may be used alternatively at the option of the cardiologist or the technician, suitable connections (not shown) being provided for this purpose. When provided for the electrocardiograph instead of the lead selector switch, the latter being omitted, the continuous-record switch is connected in the circuit as shown by the drawing of the present application. It will be noted that the time-delay means and circuit shown in Fig. l of each of my prior applications, Ser. Nos. 762,633 and 14,558 are omitted from the circuit when the continuous-record switch is used.

As illustrated, the present invention is embodied in a multiple-lead electrocardiograph but it will be readily understood that it is within the scope of my invention to apply the underlying idea to a uni-lead electrocardiograph for pre- 10 venting the transmission of -transient voltages to the electrocardiograph. Also, the invention is not to be limited to direct-writing cardiographs.

t will be understood thatthe invention may be embodied otherwise than as hereinbefore described and that various changes may be made without departing from the underlying idea or principles of the invention within the scope of the appended claims.

Having thus described my invention, what I' claim and desire to secure by Letters Patent, is:

l. For use in an electro-cardiograph which records potentials developed by the normal activities of a living body and which is provided With a plurality of channels for amplifying said potentials, said electro-cardiograph being provided also with electrodes adapted for contacting the body at spaced points on said body; circuit means interconnecting said electrodes and said channels, said circuit means including means for changeably selecting different pairs of electrodes for connection to said channels, respectively, whereby to changeably select the points on the body from which the potentials are to be transmitted through said circuit means to each of said channels, respectively, said circuit means additionally including means for blocking skin voltages of the body from said channels, said blocking means being connected to the side of said selecting means which is electrically remote from said channels, whereby the operation of said selecting means will be ineffective to discharge the voltages of said blocking means into said channels.

2. For use in an electro-cardiograph which records potentials developed by the normal activities of a living body and which is provided with a plurality of channels for amplifying said potentials, said electro-cardiograph being provided also with electrodes adapted for contacting the body at spaced points on said body; circuit means interconnecting said electrodes and said channels, said circuit means including means for changeably selecting different pairs of electrodes for connection to said channels, respectively, whereby to changeably select the points 'on the body from which the potentials are to be transmitted through said circuit means to each of said channels, respectively, said `circuit means additionally including lter means for blocking skin voltages of the body from said channels, said lter means being connected between said electrodes and the side of said selecting means which is electrically remote from said channels, whereby the operation of said selecting means will be ineective to discharge the skin voltage charge on said filter means into said channels.

3. For use in an electro-cardiograph having a plurality of channels for amplifying body-voltage variations, means for changeably connecting a plurality of pairs of leads for voltages from across diierent pairs, respectively, of different parts of the subjects body to said channels, and filter means provided with a time-constant for blocking slain voltages of the body from said channels, said filter means being connected to the side of said changeable connecting means which is electrically remote from said channels, whereby the `operation of said changeable connecting means will be ineffective to discharge the skin voltage charge on said iilter means into said channels.

4. For use in an electro-cardiograph having a plurality of channels for amplifying body-voltage vari-ations, means ,for changeably connecting a plurality of pairs of leads for voltages from across dierent pairs, respectively, of different parts of the subjects body to said channels, said means having input portions to which said voltage-variations are applied and output portions connected to said channels, and filter means for blocking skin voltages of the body from said channels, said filter means being connected to said input portions, whereby the operation of said selecting means will be ineffective to discharge the skin voltage charge on said filter means into said channels.

5. For use in an electro-cardiograph having a plurality of channels for amplifying body-voltage variations, means for changeably connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of different parts of the subjects body to said channels, said means having input portions to which said voltage-variations are applied and output portions connected to said channels, and iilter means provided with a time-constant for blocking skin voltages of the lbody from said channels, said iilter means being connected to said input portions, whereby the operation of said selecting means will be ineffective to discharge the skin voltage charge on said lter means into said channels.

6. For use in an electro-cardiograph having a plurality of channels for amplifying body-voltage variations, means for changeably connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of diierent parts ci the subjects body to said channels, said means having input portions connected to said channels, and filter means provided with a time-conm stant for blocking skin voltages of the body from said channels, said lter means being connected to said input portions, whereby the operation of said selecting means will be ineffective to discharge the skin voltage charge on said iilter means into said channels, said filter means ccmprising reactance means in series with said input potlicns and impedance means in shunt therewi 7. For use in an electro-cardiograph having a plurality of channels for amplifying body-voltage variations, means for changeably connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of different parts of the subjects body to said channels, said means having input portions connected to said channels, and filter means provided with a timeconstant for blocking skin voltages of the body from said channels, said lter means being connected to said input portions, whereby the operation of said selecting means will be ineiective to discharge the skin voltage charge on said filter means into said channels, said filter means comprising capacitance means in series with said input portions and resistance means in shunt therewith.

8. For use in an electro-cardiograph having a plurality or channels for amplifying body-voltage variations, means for change-ably connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of diierent parts of the subjects body to said channels, and i'ilter means connected in said leads to the input side of said connecting means for blocking skin voltages of the body from said channels, whereby the operation of said changeable connecting means will be ineffective to discharge the skin voltage charge on said lter means into said channels.

9. For use in an electro-cardiograph having a plurality of channels for amplifying body-voltage variations, means for changeably connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of different parts of the subjects body to said channels, and lter means connected in said leads to the input side of said connecting means, said filter means having a time-constant for blocking skin voltages of the body from -said channels, whereby Ithe operation of said changeable connecting means will be ineffective to discharge the skin voltage charge on said ilter means into said channels.

10. For use in an electro-cardigraph having a plurality of channels for amplifying body-voltage variations, 'a multi-pole select-or switch for connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of different parts of the subjects body to said channels, respectively, each of said leads being provided with a filter for blocking the -subjects skin voltages from said channels, said lter being interposed in each lead between the portion thereof which is adapted to be connected to the subjects body and the side of said switch electrically remote from said channels, whereby the yoperation 4of said switch will be ineffective to discharge the skin voltage charge on said lters into said channels.

11. For use in an electro-cardiograph having a plurality of channels for amplifying body-voitage variations, a, multi-pole selector switch for connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of different parts of the subjects body to said channels, respectively, said switch having input `contacts connected to said leads and output contacts connected to said channels, and a lter connected in each of said leads for blocking the subjects skin voltages from said channels, said filter being interposed in each lead between the end thereof adapted to be -connected to the subjects body and the end thereof connected to an input contact of the switch,.whereby the operation of the switch will be ineffective to discharge the skin voltage charge on said filters into said channels.

l2. For use in an electro-cardigraph having a plurality of channels for amplifying body-voltage variations, a multi-pole selector switch for connecting a plurality of pairs of leads for voltages from across different pairs, respectively, of different parts of the subjects body to said channels, respectively, said switch having input contacts connected to said leads and output contacts connected to said channels, and a filter connected in each of said leads for blocking the subjects skin voltages from said channels, said lter being 'interposed in each lead between the end thereof adapted to be connected to the subjects body and the end thereof connected to an input contact of the switch, whereby the operation of the switch will be ineffective to discharge the skin voltage charge on said filters into said channels, each filter comprising capacitor means in series with its respective lead and resistance means in shunt therewith.

13. For use in an electro-cardiograph which records potentials developed by the normal ac'- tivities of a living body and which is provided with a plurality of channels for amplifying said potentials, said electro-cardi-ograph being vprovided al-so with electrodes-adapted Aforcontacting the body at spaced points on said body; switching means connected between said electrodes and channels for changeably selecting different pairs of electrodes for connection to said channels, respectively, whereby to changeably select -the points on the body from which the potentials are to be transmitted to each of said channels, respectively, and capacitance and re- .si-Stance means for blocking skin voltages of the body from said channels, said blocking means being connected between each of said electrodes and the side of said switching means electrically remote from said channels, whereby the operation of said switching means will be ineffective to discharge the skin voltage charge on said capacitance means into said channels, respectively.

14. For use in an electro-cardiograph which records potentials developed -by the normal activities of ia living body and which is provided with a plurality of channels for amplifying said potenti-als, said electro-cardiograph being provided also with electrodes adapted for contacting the body at spaced points on said body; switching means connected between said electrodes and channels for changeably selecting different pairs of electrodes for connection to said channels, respectively, whereby to changeably select the points on the body from which the potentials are to be transmitted to each of said channels, respectively, and capacitance and resistance means for blocking skin voltages of the body from said channels, said blocking means being connected between each of said electrodes .and the side of said switching means electrically .remote from said channels, whereby the operation of said switching means will be ineffective to discharge the skin voltage charge on said capacitance means into said channels. respectively, a capacitance means being connected in series between each electrode and said switching means and a resistance means being connected in shunt between each capacitance means and said switching means, each capacitance and resistance means having a time-constant adapted to block said skin voltages.

15. For use in an electro-cardiograph which records potentials developed by the normal activities of a living body and which is provided with a plurality of channels for amplifying said potentials, said electro-cardiograph being provided also with electrodes adapted for contacting the body at spaced points on said body; means for changeably selecting different pairs of electrodes for connection to said channels, respectively, whereby to changeably select the points on the body from which the potentials 4are to be transmitted to each of said c-hannels, respectively, and means for blocking skin voltages of the body from said channels, said blocking means being connected lto the side of said selecting means which is electrically remote from said channels, whereby the operation of said selecting means will be ineffective to discharge the voltages of said blocking means into said channels.

16. For use in an electro-cardiograph having amplifying means for amplifying body-voltage variations from a subjects body, means in a circuit with said amplifying means for changeably selecting a plurali-ty of pairs of leads for voltages from across different pairs, respectively, of the subjects body to said amplifying means, and means for blocking skin voltages from said amplifying means, said blocking means being in the circuit with said selecting means at the side thereof electrically remote from said amplifying means, whereby the operation of said selecting means will be ineffective to discharge the skin voltage charge on said blocking means into said amplifying means.

17. For use in an elcctro-cardiograph having amplifying means for amplifying body-voltage variations from a subjects body, means in a circuit with said amplifying means for changeably selecting a plurality of pairs of leads for voltages from across different pairs, respectively, of the subjects body to said amplifying means, and skin-voltage time-constant means for blocking skin voltages from said amplifying means, said blocking means being in the circuit with said selecting means at the side thereof electrically remote from said amplifying means, whereby the operation of said selecting means will be ineffective to discharge the skin voltage charge on said blocking means into said amplifying means.

18. For use in an electro-cardiograph having amplifying means for amplifying body-voltage variations from a subjects body, means in a circuit with said amplifying means for changeably selecting a plurality of pairs of leads for voltages from across different pairs, respectively, of the subjects body to said amplifying means, and skin-voltage time-constant means for blocking skin voltages from said amplifying means, said time-constant means being connected to said selecting means at the side thereof electrically remote from said amplifying means, whereby the operation of said selecting means will be ineffective to discharge the skin voltage charge on said time-constant means into said amplifying means.

NATHAN MARCHAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,647,711 Nichols Nov. 1, 1927 1,888,139 Nichols Nov. l5, 1932 2,400,583 White May 21, 1946 

